Store-operated Ca2+ entry in insulin-releasing pancreatic beta-cells.
The fluorescent indicator Fura-2 was used to characterize the store-operated Ca2+ entry in insulin-releasing pancreatic beta-cells. To avoid interference with voltage-dependent Ca2+ entry, the cells were hyperpolarized with 400 microM diazoxide and the channel blocker methoxyverapamil was also present in some experiments. The cytoplasmic Ca2+ concentration ([Ca2+]j) of hyperpolarized mouse beta-cells was strikingly resistant to changes in external Ca2+. In cells exposed to 20 mM glucose, stimulation with 100 microM carbachol induced an initial [Ca2+]j peak followed by a sustained increase due to store-operated influx of the cation. Store-operated influx was also induced by the intracellular Ca(2+)-ATPase inhibitor thapsigargin. In the presence of store-operated influx, [Ca2+]j became markedly sensitive to variations in external Ca2+, but this sensitivity was blocked by La3+. In beta-cells exposed to both Ca2+ and Mn2+ there was slow Mn2+ quenching of the Fura-2 fluorescence, which was accelerated upon stimulation of store-operated influx. This acceleration was reversed by glucose-stimulated filling of the internal Ca2+ stores. The store-operated Ca2+ entry increased markedly during culture of the beta-cells. Activation of protein kinase C by the phorbol ester 12-O-tetradecanoylphorbol-13 acetate, inhibition of serine/threonine phosphatase by okadaic acid and inhibition of tyrosine kinase by genistein had little effect on the store-operated influx of Ca2+. In beta-cells equilibrated in 5 mM Sr2+, carbachol exposure resulted in a pronounced cytoplasmic Sr2+ ([Sr2+]j) peak due to intracellular mobilization, but little or no sustained elevation. Moreover, after activating the store-operated pathway by exposure to thapsigargin, variations in extracellular Sr2+ between 0-2 mM had only marginal effects on [Sr2+]j. Although the store-operated influx apparently accounts for a minor fraction of the Ca2+ entry, its depolarizing influence may under certain conditions be up-regulated with resulting distortion of the beta-cell function.
Liu
Y J
YJ
Department of Medical Cell Biology, Uppsala University, Sweden.
Gylfe
E
E
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D005711:Gallopamil / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007811:Lanthanum / Q000494:pharmacology; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology; D051379:Mice; D008820:Mice, Obese; D019319:Okadaic Acid / Q000494:pharmacology; D010179:Pancreas / Q000166:cytology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D013324:Strontium / Q000378:metabolism / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007328:Insulin; D019319:Okadaic Acid; D005711:Gallopamil; D008345:Manganese; D019284:Thapsigargin; D007811:Lanthanum; D002217:Carbachol; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D010749:Phosphoprotein Phosphatases; D000252:Calcium-Transporting ATPases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D016257:Fura-2; D013324:Strontium